In a manufacturing process of electronic devices such as semiconductor devices and liquid crystal displays, a substrate processing, e.g., film-forming processing for forming a predetermined film on the surface of a substrate or an etching processing for forming specific patterns to a film formed on a substrate is performed.
In the substrate processing, a plasma is used to obtain high reactivity. In particular, a plasma etching apparatus is frequently used in the etching processing. The plasma etching apparatus includes a processing chamber having a substrate therein, a lower electrode provided in the processing chamber for mounting the substrate thereon and an upper electrode provided in the processing chamber to face with the lower electrode, the upper electrode forming a shower head for injecting a gas toward the substrate mounted on the lower electrode. In this plasma etching apparatus, a specific gaseous mixture is injected through the shower head and a high frequency electric field is formed between the lower and upper electrodes to generate a plasma. The film formed on the substrate is etched by the plasma.
In the plasma etching apparatus, the etching characteristics such as an etching rate and an etching selectivity are affected by the concentration of the gas supplied onto the substrate. In an effort to make the etching characteristics uniform in the substrate plane, there have been proposed various methods for adjusting the gas distribution in the substrate plane.
For example, Japanese Patent Laid-open Publication No. 2006-165399 (JP2006-165399A) discloses a technique in which the gas distribution is adjusted by supplying an arbitrary gaseous mixture to a plurality of locations in a processing chamber with a relatively simple line configuration. Japanese Patent Laid-open Publication No. 2007-207808 (JP2007-207808A) discloses a technique in which the gas distribution is adjusted by supplying an arbitrary gaseous mixture to a plurality of locations in a processing chamber with a simple line configuration and through a simple control operation, wherein a processing gas is split to flow through first and second paths so that it can be injected from first and second portions of a shower head, respectively. Further, a specific additional gas is allowed to flow through these paths, thereby adjusting the ingredient and flow rate of the processing gas. Japanese Patent Laid-open Publication No. 2007-214295 (JP2007-214295A) discloses a technique in which the gas distribution is adjusted by supplying an arbitrary gaseous mixture to a plurality of locations in a processing chamber with a simple line configuration and through a simple control operation, wherein a processing gas is split to flow through first and second paths so that it can be injected from first and second portions of a shower head. Independently of the processing gas, a specific additional gas is injected to thereby adjust the ingredient and flow rate of the processing gas with an increased degree of freedom.
However, requirements for in-plane uniformity of the substrate become more and more strict. In particular, it is difficult to correct the characteristics of an outermost circumference of a peripheral edge of the substrate. Therefore, it sometimes happens that the in-plane uniformity is not sufficiently secured by merely employing the techniques mentioned above. Further, there happens sometimes that the additional gas is not needed depending on the process. In case where an additional gas line is separately provided as in JP2007-214295A, there is a possibility that, if the additional gas is not supplied, a deposit may be accumulated in injection holes through which the additional gas is to be injected and an abnormal electric discharge may be generated in the vicinities of the injection holes.